Despite successful elections last year that were seen as a step toward reconciliation after years of civil conflict, the government and a 13,000-strong United Nations peacekeeping mission have struggled to contain killing sprees by rebel groups.

The Union for Peace in Central African Republic (UPC) rebels carried out the killings on Dec. 12 in the town of Bakala, where they had been fighting the Popular Front for the Renaissance of Central African Republic (FPRC), HRW said in a statement.

The UPC lured 25 of the civilians to a local school where it shot them after killing seven others earlier the same day, HRW said. At least 29 other civilians have been killed in fighting around Bakala since late November, it added.

“They certainly feel emboldened to commit worse and worse crimes,” said HRW researcher Lewis Mudge of the rebels in an interview, adding the civilians were likely targeted because they were thought to be allied with rival groups.

Both the FPRC and UPC are former members of the mainly Muslim Seleka rebel alliance that united to oust then-President Francois Bozize in 2013, sparking backlash from Christian anti-balaka militias.

But the two groups have since fallen out over competition for territory and control of tax revenues. The Muslim FPRC are now allied with the Christian anti-balaka, an indication of the waning role of ideology in the conflict.

On Wednesday, the government appointed a prosecutor to a U.N.-backed special criminal court created to investigate war crimes and crimes against humanity, a potential first step toward bringing rebel leaders to justice.